The full sandbox should be refreshed after each major release to production. This way, the full sandbox will have the most updated data and metadata from the production org, and can be used for final load and regression testing before the next release. Option A is incorrect because refreshing the full sandbox after user acceptance testing is complete is not necessary, as user acceptance testing can be done in the partial data sandbox or the production org. Option B is incorrect because refreshing the full sandbox after each push from the partial data sandbox is not necessary, as the full sandbox can receive configuration and code changes from the partial data sandbox without refreshing. Option D is incorrect because refreshing the full sandbox after a new user is added to production is not necessary, as adding a new user does not affect the data and metadata in the full sandbox.

To track the total number of trails associated with a park without writing code, the correct actions to take are:
Use a roll-up summary field on the Park record to show the total number of Trails (B). Roll-up summary fields calculate and display a value in a master record based on the values of fields in a detail record. They are used to count, sum, average, or get the minimum/maximum of values in related detail records.
Use a master-detail relationship between the Park and Trail objects (C). Master-detail relationships are necessary for roll-up summary fields as they allow the master object to control certain behaviors of the detail object and summarize data from those detail records.
A formula field (A) cannot dynamically count related records unless those records are linked via a master-detail relationship, and it cannot alone handle counts across related records without such a relationship. A lookup relationship (D) does not support roll-up summaries unless combined with additional tools like triggers or third-party apps, which involve coding or extra configuration outside standard object setup.
For more details, refer to the Salesforce Help documentation on master-detail relationships and roll-up summary fields:
Master-Detail Relationship: https://help.salesforce.com/articleView?id=relationships_considerations.htm&type=5 Roll-Up Summary Fields: https://help.salesforce.com/articleView?id=fields_about_roll_up_summary_fields.htm&type=5

To provide a help guide to enable reps to easily get help where needed during the different sales processes, an app builder should recommend Path. Path is a component that displays the key fields and guidance for each stage of a sales process on an object's record page. Users can see where they are in the process, update the stage and fields, and access resources such as tips and links. [Source]

AppExchange and Apex Code are two resources that can provide custom components for a Lightning app. AppExchange is a marketplace where developers can publish and sell their custom components or apps. Apex Code is a programming language that can be used to create custom components or logic for a Lightning app. Import Wizard and Visualforce are not resources for custom components, but tools for data import and web page development respectively.

Marking stage dependent fields as required on the Opportunity page layout is a good solution to improve efficiency and data quality, as it ensures that users enter the necessary information for each stage of the sales process. Adding a Path component with fields and instructions aligning to stages on the Opportunity is another good solution to improve efficiency and collaboration, as it provides guidance and best practices for users to move the Opportunity along the sales cycle. Using two Tabs components to separate record information from activities may not be an optimal solution, as it may reduce the visibility and accessibility of important data. Setting up an approval process requiring manager consent at each stage of the Opportunity may not be a feasible solution, as it may introduce unnecessary delays and complexity in the sales process